The present invention relates to sawmill apparatus provided with vertically moving log engaging dogs, and particularly to such apparatus for accurately moving the log engaging dogs without binding and without misalignment.
In known sawmills, a log is engaged endwise between a pair of dog members and propelled through a saw for severing the log into a plurality of boards and cants. Sawing may be accomplished as the log moves in both forward and reverse directions through a saw, with the saw blade being repositioned between first and second passes. The log is conventionally delivered between the log engaging dogs by conveyor means having some vertical adjustment so the dogs can engage a log approximately midway of each end despite the varying diameter sizes of logs that may be encountered. The dogging members themselves are usually not vertically movable, but may be positioned at such height that the largest log encountered will have its lower perimeter placed well above the lower saw guide for avoiding any damage to the saw apparatus. Unfortunately, this can produce considerable drop in the cants or boards sawn from the log as they fall onto an outfeed conveyor therebelow, resulting in damage to the lumber as well as possible damage to the equipment.
While mills have been previously constructed with vertically movable dogs, e.g. employing a vertical ball screw for producing the vertical adjustment, operation thereof has not been entirely satisfactory because of the considerable weight required of a dogging apparatus if it is to successfully engage and hold a log. Thus, prior apparatus has been unable to raise and lower the dogs without binding and operating inaccuracies or actual stalling of the equipment. Moreover, when dogging apparatus is made vertically adjustable, difficulties are encountered due to side movement of the dogging apparatus because of the narrow profile necessary for passing through the sawing apparatus, resulting in inaccurate sawing.